Every farm needs a good farm dog. If you’re looking for one, it’s probably a good idea to decide first just what kind of farm dog you want, although you could try a google search of “farm dogs for sale” and see what you come up with.
Decide first what you need the dog to do. Is it just for companionship? Or do you want it to act as a livestock guardian dog? Do you need a dog to herd animals? Most dog breeds are better at some things than others, so pick one that most closely matches what attributes would be most useful on your farm.
Once you choose your breed, try finding a national organization online for that breed. Most of them have sections listing breeders, or giving you an idea where to find a dog. You can also try a rescue dog, but if this is your first dog, I wouldn’t recommend it. Sometimes it’s a little more difficult to re-train an older dog than start with a puppy.
Good luck with your search!